Colombia's president has said peace negotiations with the Farc rebels are being arranged after secret talks between the government and leaders of the guerrilla movement.

Following a week of growing rumours, President Juan Manuel Santos confirmed in a national television address on Monday night that his government has been conducting "exploratory talks" with rebels of the Revolutionary Armed Forces of Colombia to seek an end to an insurgency that has lasted five decades.

Santos did not confirm the timing but said that "in the coming days" he would reveal details of the outcome of the initial talks. Several media outlets reported that the two sides could begin formal negotiations as early as October and that the venue could be Cuba or Norway. Venezuela's President Hugo Chávez has reportedly been acting as a facilitator for the preliminary talks.

The last time time the Farc sat down to peace talks in 1999 the government granted the rebels a 42,000 square kilometre swath of land as a safe haven in which to conduct the negotiations. But after two years the Farc were stronger, larger and bolder than ever in their attacks on the military and civilians. Talks broke down in 2002 after the Farc hijacked a commercial plane and kidnapped a senator.

"We are going to learn from the errors of the past," said Santos in a clear reference to those failed talks. "Any [peace] process has to lead to the end of the conflict, not prolong it."

Even as preliminary talks have been going on the Farc have stepped up their attacks in an apparent show of strength before discussing peace. According to the defence ministry acts of "terrorism" were up 53% in the first seven months of this year compared with the same period last year. On Sunday a car bomb blamed on the Farc killed six people including two children in the south-eastern town of Vistahermosa.

But the guerrilla leadership has been making peace overtures for months. In January the Farc's new senior leader, Rodrigo Londoño, also known by the alias Timichenko, called for talks and then announced an end to kidnapping for ransom, which had been one of the government's demands.

In April the group released the last 10 of its security force hostages, some of whom had been held for 14 years. The government then got congress to approve a constitutional amendment that lays the legal groundwork for an eventual peace process with rebels.

The country's second-largest guerrilla group, the National Liberation Army, or ELN, told Reuters on Monday that it would join the Farc in peace talks with the government.